N-Insertion reaction mechanisms of phenyl azides with a hafnium hydride complex: a quantum chemistry calculation

Abstract

Density functional theory (DFT) calculations were performed to investigate the detailed mechanisms for the N-insertion reaction of phenyl azides with a hafnium hydride complex. This reaction involves an intermolecular hydride transfer from the hafnium center of complex 1 Cp₂*HfH₂ to the terminal nitrogen atom of a phenyl azide. Subsequently, a 1,3 hydrogen shift from the N1 atom to the N3 atom takes place, accompanied by cleavage of the N2–N3 bond to provide amido complex 3 Cp₂*HfH(NHPh) and dinitrogen. A further reaction is related to the intermolecular hydride transfer from the hafnium center to the N1′ atom of a second phenyl azide, followed by the formation of the final product, bis(amido) complex 9 Cp₂*HfH(NHPh)₂via the liberation of the second dinitrogen, which is the rate-determining step with an overall barrier of 29.8 kcal mol⁻¹. Frontier molecular orbital theory analysis shows that phenyl azides are activated by nucleophilic attack by the hydride ligand, which is consistent with our previous studies of N₂O activation by other transition-metal hydride complexes.